JP-A-2008-54439 discloses an electric power system. The electric power system of JP-A-2008-54439 has a configuration in which a cable is extended from a vehicle equipped with a power accumulating device, and the connector of the cable is connectable with a connector coupled to a power line cable equipped in a residence. In this configuration, the vehicle and the power line cable in the residence are enabled to transfer alternating-current electricity through an electricity supply system including these cables and both the connectors.
In this configuration, the vehicle is equipped with a conversion device configured to implement DC-AC conversion and voltage conversion. When the power accumulating device is charged with electricity and discharge electricity, electricity is transferred by using the electricity supply system and the conversion device. In the configuration of JP-A-2008-54439, in both cases where the power accumulating device equipped in the vehicle is charged with electricity through the power line cable in the residence and where the power accumulating device discharges electricity through the power line cable, the electricity is transferred through the same electricity supply system and by using the voltage conversion device.
In general, it is desirable to supply stable electricity, which is significantly constant in properties such as voltage, into an alternating-current power line installed in a building for supplying alternating-current electricity to an electric load connected with the alternating-current power line. To the contrary, a power accumulating device equipped in a vehicle is configured to supply electricity, in general, having a large fluctuation due to influence of an external environment.
In the electric power system of JP-A-2008-54439, the power accumulating device equipped in the vehicle may be charged with electricity without a significant difficulty. Nevertheless, in the configuration of JP-A-2008-54439, when the power accumulating device discharges electricity into the alternating-current power line in a building through the same electricity supply system by using the same conversion device, the alternating-current power line may be exerted with an adverse effect due to unstability of the discharged electricity.
In order to solve such an adverse effect, it is conceivable to modify the conversion device in the vehicle into a highly efficient device and/or to provide an additional device into the electricity supply system between the vehicle and the alternating-current power line in a building in order to stabilize electricity. Nevertheless, in both the cases, a complicated device is needed for stabilizing discharged electricity.